JP2022017415A - Method for further smoothening flexographic printing color tone reaction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system for improving a color tone reaction curve of a printing plate, that is a system for performing flexographic printing and a method thereof, and such a method including a plate making method.

SOLUTION: A method according to the present invention includes a step at which a screen having a resolution, that is defined by a basic pattern of an equal size screen spot, is provided. Each screen spot includes a minimum light exposure individual element represented on the screen. In at least a non-solid color tone part of a printing plate or a mask, a physical spot size is selectively adjusted so that each set of four adjacent physical spots of the basic pattern has an unexposed area at a center therebetween. Each physical spot corresponds to resolution power of laser beam which exposes the spot onto the mask. An image formation step includes a step at which laser beam output is increased for an isolated pixel rather than a non-isolated pixel. Further, disclosed are a mask and a printing plate, and an image formation system for creating the mask and the printing plate.

SELECTED DRAWING: Figure 4B

COPYRIGHT: (C)2022,JPO&INPIT

Description

Cross-reference to related applications This application claims the priority of US Provisional Patent Application No. 62 / 342,475 filed May 27, 2016. This US provisional patent application is incorporated herein by reference in its entirety.

The present invention relates to printing, and more specifically to a system that implements such a method including flexographic printing, a method thereof, and a plate making method, and is a system for improving a color tone reaction curve of a printing plate.

Traditionally, flexographic plates have a flat top surface for printing solid areas, a flat bottom surface for leaving an unprinted substrate, and an upper layer (physical contact with the printing medium on which the printed image is transferred). Layers) with a large number of mathematically organized print dots. One of the printing methods is called AM (Amplitude Modulation) and is characterized by having a fixed number of dots per linear inch called screen ruled lines or line art. Over time, stochastic screening (also known as FM screening, where the dots have a constant size and the density or frequency of the dots is modulated), and typically highlighting has a stochastic pattern, and the rest. Many variants have been developed, including hybrid AM / FM screening according to conventional AM patterns.

Methods have also been developed to improve solid rendering by replacing flat surfaces with modulated surfaces. Currently, mathematical grids, and more probabilistically, lines / grooves, and more recently, numerous squares or squares organized into very high resolution patterns or textures that can bring up to less than 50% of the printing plate. Several modulation patterns are commonly used, including round "white" cells.

As a result of research to find the best solid rendering pattern, further improvements in the imaging device (especially significant remote level control over the microscopic results of the resulting print plate) have resulted in significant solid enhancement. Increasing the concentration by 0.3 on the density scale is no exception (eg, achieving a cyan concentration of 1.2 without a solid pattern and 1.5 with a solid pattern). In addition, such improvements also typically result in a color shift towards a hue closer to the theoretical hue of the ink. This is due to the thin ink layer and is now generally accepted as a result of high frequency modulation.

However, this realized advantage raises new issues. The significant enhancement of solid rendering creates a strong discontinuity between solid and near solid. This discontinuity can occur even in synthetic tones (such as those created through the tonal features of applications that generate PDF gradation structures, such as Adobe Illustrator) (using different separation methods). In addition to the density that can be maximal for a given ink, it is often visible in continuous tones (allocation of a density that smoothly declines from this density to a particular area) in close areas. The human eye is very sensitive to this discontinuity. As a result, this problem leads to the rejection of printed works.

Several mitigations to this discontinuity problem have been proposed and are widespread. One such mitigation measure is to avoid using solid patterns where smooth gradation is required. This means that, in practice, the algorithm or human operator decides what to treat as solid (to be augmented) and what to treat as non-solid. One of the methods is to accept only the uniform hue of the composition as solid and the rest (contone, gradation) as non-solid. This is a simple, reasonably practical method (some RIPs can do this automatically). However, the disadvantage of this method is that it can lose the advantage of enhancing rendering in critical locations. For example, without enhancement, the contone may be in a "dull" state, i.e., printing may continue in a limited color range. Highly saturated colors may not be reached because the saturated colors often contain at least one printing ink with high density. Ultimately, in many designs uniform regions are combined with variable regions. Syntheticly different treatments with uniform shades compared to other areas may again show discontinuity in the final print result. To detect this type of discontinuity requires a highly specialized (usually slow) algorithm to scan the entire page description, and even if it is detected, there may not be a suitable solution.

Patent Document 1 (European Patent No. 1557279B1) (Dewite) proposes another mitigation measure for the discontinuity between the solid region and the substantially solid region, and in at least one embodiment, the solid pattern , More specifically, the groove fades to the screened area. This mitigation measure can also be adjusted to avoid the possibility of unwanted side effects, such as the generation of moiré patterns. Using mathematics, it is taught that a combination of two patterns with different frequencies and / or angles can produce a third pattern with reduced borders and angles. This moiré pattern is often so noticeable to the human eye that it can be rejected by print buyers. Dewite's method solves this by placing the solid rendering pattern "rationally multiple times" the original pattern. That is, the solid rendering pattern is selected so that the moire generated by the original screen pattern has the same frequency and angle as the original screen. Assuming the original screen is acceptable to the human eye, the combined effect is also generally acceptable.

However, since very well calculated frequencies and angles for the solid enhancement pattern must generally be selected to avoid the moiré pattern, the frequencies and angles selected to avoid the moiré pattern are solid enhancement. May not be optimal for. In general, non-moiré generation patterns can, on average, enhance solid by half the optimal enhancement pattern.

In addition, the very non-linear behavior of plate making and printing of flexographic printing plates is that if the solid pattern fades to a nearly solid screening area, the resulting color curve will always be linear, as desired. It means that it does not always fade to. In general, for example, half of the pattern does not necessarily increase half of the concentration, it may not increase at all, or it may even work the other way around. Also, the addition of conventional screen dots can disrupt the pattern so that it no longer works as desired. Attempting to keep the patterns undisturbed by the screen dots by maintaining protected zones between the patterns may add additional complexity at the risk of further interfering with the solid rendering effect.

Another very well-known problem in flexographic printing is the problem of (close) dot contact. Ink rendering for flexographic printing can react very non-linearly when the print dots are within certain thresholds that are close to each other. Two dots that are relatively close to each other may form a "bridge" that is close to the printing surface that holds what should be the non-printing area between the dots is ink, and sometimes even more ink than the printing area. This can lead to strong "tonal jumps" at unpredictable concentrations. Until a certain threshold is reached, any threshold can be affected by a number of variables that are not always known or predictable, and the ink bridges between two adjacent dots. Does not form. Second, when the distance between the dots is reduced to a minimum, bridges may suddenly form. The formation of bridges can depend, among other things, on printing pressure, dot shape, anilox characteristics and pressure, ink viscosity and printing speed.

Aspects of the invention according to claim can alleviate the problem of bridging near dots, at least in part, by affecting the shape so that the bridge formation is not abrupt and the ink is low. Aspects of the claimed invention can simultaneously alleviate the discontinuity between the solid region and the substantially solid region.

European Patent No. 1557279B1

One aspect of the present invention is a method for producing a flexographic printing plate or a mask for producing a flexographic printing plate. One step in this method is to provide a screen with the resolution defined by the basic pattern of screen spots of the same size. Each screen spot contains the smallest exposed individual element represented on the screen. The printing plate or mask selectively adjusts the size of the mask corresponding to the physical spot or screening spot on the printing plate in at least a part of the printing plate or mask corresponding to the non-solid color region of the printing plate. , Each set of four adjacent physical spots in the basic pattern is created by having an unexposed area in the center between them. In one embodiment, each screen spot in the basic pattern includes isolated pixels, including exposed pixels surrounded by eight unexposed pixels. In such an embodiment, each screen spot can include a single pixel, and each physical spot can correspond to the resolution of the laser beam used to expose the spot on the mask. The method further comprises the step of imaging the mask with a laser beam. The step of imaging a mask with a laser beam enhances the output of the laser beam used to image each separated pixel against the output of the laser beam used to image the unseparated pixels. It may include a step to do. Even if the size of the unexposed area between the four adjacent imaging spots is optimized by adjusting the output of the laser beam corresponding to each imaging physical spot for optimization of ink transfer during printing. good.

The method of forming the screen includes a step of forming a first screening supercell for each pixel located at (X, Y) in the first screening supercell, and a first mathematical formula (X'= fx). (X, Y); the step of assigning a position (X, Y) in the second screening supercell by applying Y'= fy (X, Y)), followed by the first formula. It may include a step of setting a value in a second supercell that is not an empty pixel value. In the first formula, (i) X'and Y'are integers, (ii) the two pixels of the first supercell are not converted to the same pixel in the second supercell, and (iii) all. A set of rules that pixels (X', Y') are on a high resolution basic pattern in which the pixels surrounding each pixel (X', Y') are at least eight empty pixels that are not filled with a mathematical formula. To comply with. The first supercell has the number of lines (Lpi'= f3 (Lpi)) and the angle (Ang') by applying fx (X, Y) and fy (X, Y) in the second supercell. = F4 (Ang)) can have a number of lines (Lpi) and an angle (Ang) so that it can be generated. For the desired Lpi and desired Ang of the second supercell, the inverse transformation formula (Lpi ″ = f3-1 (desired Lpi), Ang ″ = f4-1 (desired Ang)) is applied to the line. Generate a screen with a few Lpi "and an angle Ang".

Screens with multiple screens, each corresponding to one ink color, do not have the step of calculating Lpi ″ and Ang ″ of each screen and secondary moire for the desired number of lines and angles per set. , A step of identifying closely matching borders / angle sets, a step of generating multiple first screening supercells corresponding to closely matching borders / angle sets, and a plurality of first screening supercells, respectively. Can be generated by the step of converting to the corresponding second screening supercell. The second supercell is created so that the third supercell has the same size and the same desired borders and angles as the second supercell, so that the third supercell improves highlighting. The second and third supercells may be integrated into the fourth supercell, corresponding to the screen to be configured and to have a size and desired borders and angles. This integration involves (a) for each pixel, a step of determining which cell the pixel belongs to, and (b) which of the second and third supercells copies the information based on the determined cell. Achieved by performing an operation including (c) a step of copying information from the second or third supercell determined in step (a) to the fourth supercell. May be good. The determination in step (b) may be a random determination performed using the blue noise determination, but may be a random determination without limitation, or may be systematic. The method may include a step of copying information from the second supercell at a relatively high color density and a step of copying information from the third supercell at a relatively low color density. a) to (c) may be performed on the entire threshold array. The third supercell can be generated by applying the second formula (X'= fx (X, Y); Y'= fy (X, Y)), where the second formula is the first. It is different from the formula in, but adheres to the same rules.

This method switches to a highlighting improvement technique, eg, by applying this method to the original screen that embodies the highlighting improvement technique in at least part of it, or to solid AM dots at a particular highlighting level. May be used in combination with some techniques.

Another aspect of the invention includes a flexographic printing plate or a mask for making a flexographic printing plate manufactured by any of the methods described herein. The resulting print plate or mask may have one or more regions with a first high resolution basic pattern and one or more regions with a second high resolution basic pattern.

Yet another aspect of the invention includes an imaging system such as an image setter that manufactures a mask for making a flexographic printing plate. Such an imaging system comprises a laser source configured to expose a portion of the mask to radiation corresponding to the individual spot identified in the imaging data file. The laser source has an adjustable laser output for adjusting the image spot size on the mask. The imaging system also comprises a controller with a processor configured to receive imaging data and convert it into operating instructions for a laser light source. The imaging data includes a screen having a resolution defined by a basic pattern of screen spots of the same size. Each screen spot contains a minimal exposure individual element represented on the screen. The controller is such that each set of four adjacent physical spots in the basic pattern has an unexposed area in the center between them in at least part of the printing plate or mask corresponding to the non-solid color area of the printing plate. It is configured to produce a printing plate or mask by selectively adjusting the size of the physical spots produced by the laser on the mask corresponding to the screening spots. The exposed spots of the imaging data include isolated spots, and each isolated spot includes an exposed spot surrounded by eight unexposed spots. In this case, the controller identifies the isolated spots and corresponds to the isolated spots in the imaging data that are relatively larger than the output that produces the imaging spots corresponding to the non-isolated spots in the imaging data at the laser source. It is configured to instruct to use an output that produces an imaging spot. In particular, the physical spots corresponding to the imaging data may include circular spots that do not completely overlap each other.

An exemplary high resolution basic pattern is shown. An exemplary high resolution basic pattern is shown. An exemplary high resolution basic pattern is shown. An exemplary high resolution basic pattern is shown. An exemplary high resolution basic pattern is shown. Shown is an exemplary screened area formed from an exemplary high resolution basic pattern. Shown is an exemplary screened area formed from an exemplary high resolution basic pattern. A conventional supercell having a conventional AM dot is shown. Shown is a supercell with corresponding dots defined by an exemplary high resolution basic pattern. Shown is a supercell with corresponding dots containing another exemplary high resolution basic pattern. Indicates a supercell. Shown is a portion of an exemplary screen containing a combination of "solid" dots and dots defined by isolated pixels. Shown is a portion of an exemplary screen containing dots defined by isolated pixels from which dots at certain positions have been removed. Tones below the critical gradation level indicate the original transition screen modulated by removing the dots. FIG. 7 shows a new transition screen after converting the screen of FIG. 7A to use isolated pixels. Shown is a screen of a combined supercell with two different distributed grid patterns. An exemplary stochastic screen consisting of isolated pixels is shown. An exemplary stochastic screen consisting of isolated pixels is shown. FIG. 3 is a photomicrograph of print dots formed using a printing plate created using a standard AM screen. FIG. 3 is a photomicrograph of printed dots formed using a printing plate created using an exemplary screen with dots consisting of isolated pixels. Shown is a screen with conventional AM dots composed of 20 exposed pixels. Shown is a screen with dots, each consisting of four isolated exposed pixels. Shows an exemplary screen over a large tonal range, with various sections magnified and highlighted. Shown is an exemplary highlight area of a screen consisting of a combination of solid AM dots and dots consisting of isolated exposed pixels. FIG. 3 is a photomicrograph of print dots formed using a printing plate created from the screen pattern shown in FIG. 13A according to an embodiment of the present invention. The 3 × 3 structural block used for the detection of the isolated pixel is shown. Shown is a collection of four adjacent pixels indicating an area exposed by the laser corresponding to each pixel at an exposure level that does not cause overlap of the exposed areas. A collection of four adjacent pixels showing the area exposed by the laser corresponding to each pixel is shown using a laser output intended to sufficiently overlap each exposed area to produce a solid dot. 15A and 15B show a collection of four adjacent pixels indicating a laser-exposed area corresponding to each pixel at the laser exposure level between the pixels, leaving an unexposed area in the center. It is a schematic diagram of an imaging system.

One aspect of the invention is from a very high resolution basic pattern of individual imaging spots exposed with a laser output adapted (typically even higher) than the laser output conventionally used in the art. Includes solving or mitigating the above problems by using screening patterns constructed on most of the tonal scales. As a result, the actual screen shape (eg, circular dots) becomes a virtual shape on the digital film and printing plate, producing the actual print dots with less of the above drawbacks, and further to the enhanced solids. Produces a smooth gradation.

In a preferred embodiment, the high resolution base pattern may be equal to the pattern used for solid rendering. One such pattern is shown in FIG. The square grid 100 is a high resolution grid (eg, 4000 ppi) of the imaging system. The laser forms an image of the black point 102 and does not form an image of the white point 104. As a result, in the black LAMS layer, black spots are removed so that such regions generate dot formation. By adjusting the laser output, the size of the removed black spots can be adjusted to optimize dot formation for ink transfer in the printing process. The solid ink density (SID) can be optimized by selecting the size of the black spot corresponding to the peak of the SID for a specific series of operating conditions (ink viscosity, constituent material of the substrate that receives the ink, etc.). The white part is not exposed and the surface of the printing plate is formed under the uppermost part. However, because of the very high frequency, the underside of the white area is still much higher than the unprinted low levels. In practice, the height difference between the white zone and the black zone may be only about 50 micrometers (although the total relief often exceeds 500 micrometers).

The pattern shown in FIG. 1A, as is well known in the art, can produce very high solid densities only when and only when the black spots are imaged with a well-tuned laser output. It's just one of many known patterns. The patterns shown in FIGS. 1B to 1E are the same as those described with respect to FIG. 1A above, as long as the patterns have black dots separated from each other (meaning that none of the eight pixels surrounding the black dots are black). Can be used in a way.

The solid area is just after the basic pattern. For the screened area, imaging still occurs only at the black spots determined by the high resolution grid. However, due to the reduced density, some of the sunspots are no longer imaged. (On the other hand, all white points are still not always imaged). This produces a screened area as shown in FIG. In this region, each collection 200 of sunspots 102, each representing, for example, one shot of laser power, resembles a conventional "screening dot" as would have been rendered according to prior art. After creating a print plate and printing such dots, print dots that approach the shape of the print dots of the prior art but have better characteristics will be created.

This advantage can be understood by studying the actual typical print shape of flexographic dots, for example on a plastic substrate, as shown in FIGS. 10A and 10B. 10A and 10B show micrographs of a patch of dots printed on a film with black ink using gradation levels (not colors) at halftones (ink crosslinks). FIG. 10A shows dots formed using a standard AM screen. FIG. 10B shows dots formed using the exemplary screens described herein.

Effect of Dots on Tonal Jumps in Contact Here, referring to Figure 3, human imagination sees the dots as continuing their bridging behavior (spots are on individual high-resolution grids). The actual print spots are never continuous (because they are imaged). Inspection of many substrates reveals that this reduces ink cross-linking. While some bridges may still be formed, such bridges grab an excess of ink that typically works with the traditional approach where each screening dot is rendered as a solid part. There is nothing to do.

By providing eight empty pixels around each laser pixel, the resulting pattern does not, by design, cover the printing plate area. However, experiments have shown that the best solid rendering is achieved by optimizing the laser output applied to the distributed pixels. In practice, the laser output and pixel pattern should ideally be coordinated with each other. The fact that the pixels are dispersed allows for such adjustments with very few, if any drawbacks. Can the imaging system simply optimize the laser power (higher power commonly used) for the entire printing plate if the entire printing plate contains dispersed pixels as described herein? Or a more sophisticated system can automatically detect areas where the laser output needs to be optimized based on the fact that the dots are scattered and in the expected position. Those skilled in the art know how to adjust the laser output, such as the PixelBoost functionality available in Esk's Graphoras user interface. This interface uses, for example, an Esco CDI imaging device upgraded to "UV Flattop Option". The CDI imaging device includes, for example, an upright optical head and a Gradient Index (or Aspheric) "lens. Drums with LUST servo drives use the "Flattop" exposure profile associated with the "High Res" option. The "High Res" option is described, for example, in the 4th edition of the Esco Technical Memo dated March 11, 2011, entitled "Upgrade to Flattop / Round Top Option". This technical memo is incorporated herein by reference. The above features are also standard in the Esco CDI Crystal system.

Part of an exemplary imaging system comprising a laser source 1600, a processor 1602 controlling the laser source, and a memory 1604 for storing an imaging data file corresponding to a screen as described herein. Is shown in FIG. The laser source 1600 has an adjustable laser output for adjusting the imaged spot size on the mask. The controller 1602 typically comprises one or more computer processors programmed with instructions, and may also include hardware control. The controller is configured to receive the imaging data and convert it into operating instructions for the laser source, selectively adjusting the size of the physical spots generated by the laser on the mask according to aspects of the invention. May include that. Thus, imaging data comprising screens having a resolution defined by the basic pattern of uniformly sized screen spots, wherein each screen spot contains the smallest exposure individual element represented on the screen. If so, the laser creates a physical spot on the mask corresponding to the screening spot. As is known in the art, the mask is then used during the UV exposure step to expose the print plate, which is further processed to form the finished print plate. The printing plate or mask produced by the method described herein produces a printing plate in which each set of four adjacent physical spots in the basic pattern has an unexposed area in the center between them. The "minimum exposure individual element represented on the screen" may be a pixel such as the system described herein that utilizes isolated pixels, or a pixel corresponding to the smallest dot used in a low resolution screen. It may be a gathering. For systems that utilize isolated pixels, the controller identifies the isolated pixels and sufficiently augments the isolated pixels to leave an unexposed portion in the center of each set of four exposed isolated pixels (software and /). Or it consists of hardware). In the case of a system using a reduced resolution screen, the system correlates with each pixel such that each collection of the four smallest exposed individual elements (eg, dots) has the appropriate unexposed portion of them. It may be configured to adjust a certain laser output. At this time, the controller does not need to identify the isolated pixel.

The screen described herein may be configured by utilizing a conventional screen and perforating the screen with a desired high resolution basic pattern. Perforation may require, for example, an algorithm in which each pixel of a conventional screen is compared to the corresponding pixel of a high resolution pattern. If both are black, the resulting pixel will be black, otherwise it will be white. The described method is hardware programmed only to image solid pixels by overlaying films or according to a high resolution basic individual pattern (thus ignoring any other black pixels). Corresponds to the methods that can be achieved by using the device.

While easy to implement, the above method may have some drawbacks. The first drawback may be the occurrence of unwanted moire patterns. Modern high quality screen dots are carefully designed to create nearly equal surfaces of dots and to more or less mathematically correct the average position of the dots. When pixels are removed according to a high resolution pattern, certain dots may lose / retain more pixels than other dots, and the average position may shift slightly. This can occur rather systematically according to the mathematical interference pattern between the original screen and the high resolution basic pattern, which becomes visible to the human eye and rejects the print result. It leads to.

The second drawback can be the loss of gradation level. In the simplest case, the screen may have as many gradation levels as there are pixels in one print dot. A more complex approach is to size the print dots so that the total average gradation level increases in much smaller steps (at the cost of the slight modulation added to the pattern, with the risk of becoming visible). Adjustments create additional gradation levels. In practice, such modulation is applied using a blue noise pattern so that the visibility of the modulation is minimized. However, multi-layer blue noise patterns can break conventional rules. Based on the system of interference, certain gradation levels may risk losing their all additional dots, while other gradation levels may retain their all additional dots. This creates a "staircase", with some steps being strongly compressed while others being expanded.

However, the screen can be ideally configured without the above drawbacks while still producing the expected borders and angles. The screen construction method of the present invention uses conversions with different ruled lines, angles and resolutions from a specially designed basic screen. This screen is transformed into a desired screen with the required borders and angles by the method described below.

The operations discussed below are preferably performed on a screen supercell (also known as a threshold array). In a preferred embodiment, supercell screening with a threshold sequence is used. By applying the same logic, similar results can be obtained with other screening methods, but some methods may require RIP of the page description at different resolutions and angles, but the supercell method There is no such requirement.

4A-4C show the conversion of a conventional supercell into a supercell suitable for carrying out the present invention. 4A-4C show supercells with only one screen dot for ease of explanation, but the same logic can be applied to supercells of any size or angle. Also, while the description is provided with reference to a pure bitmap, the supercell has a threshold for each pixel, which does not change the logic, and this method is a bitmap sequence screening method. It is shown that it can also be applied to.

FIG. 4B shows an example of utilizing a very high resolution pattern called DDWSI. FIG. 4C shows an example of utilizing a slightly lower pattern called WSI at 45 degrees. In the DDWSI example, for each pixel in the original supercell, the position in the new supercell is found by applying the shape formula.
X'= fx (X, Y)
Y'= fy (X, Y)

The value of the new supercell pixel found is equal to the value of the original supercell pixel. For binary inputs, the output is binary. For the threshold array, the threshold is copied. This does not fill the entire new supercell. Unreachable pixels are set to maxThresholdValue + 1 in the threshold array (in the case of binary bitmaps) white or (indicating pixels that never turn black).

The functions fx and fy have the following characteristics.
-Results X'and Y'are integers.
-If the input is different, the output will be different (two pixels of the original grid will not be converted to the same pixel in the output grid).
-All output pixels (X', Y') are on the high resolution basic pattern.
-Around each output pixel, there are eight pixels that are never reached by conversion.

Therefore, a pair of functions (fx, fy) determine a high resolution basic grid. Two such function pairs that produce the results shown for the input dots of FIG. 4A are shown in FIGS. 4B and 4C.

The function is:
In the DDWSI pattern (Fig. 4B),
Fx (X, Y) = 2X
Fy (X, Y) = 2Y
In the WSI pattern (Fig. 4C)
Fx (X, Y) = 2X + 2Y
Fy (X, Y) = 2X-2Y

In some cases, the shape of the virtual dot is maintained in a large state, and in other cases, the shape undergoes even greater changes. However, the following generally apply:
-Two equally sized dots are converted into two equally sized virtual dots (each with the same number of black dots).
-Continuous dots are converted into dots with "virtual" continuity. The approximate value of the circle will be converted to the approximate value of the circle. The same applies to rectangles, and the same applies to stochastic patterns with specific approximate features.

The above operation is performed on each pixel in the supercell, leading to a new supercell that is generally larger than the original supercell. When the original supercell is characterized by two natural numbers A and B (as shown in FIG. 5), a new supercell can be found by utilizing the outer boundaries of the transformed pixels.

According to the same logic, the borders and angles of the screen change under this operation (assuming they have the same resolution).
Lpi'= f3 (Lpi)
Ang'= f4 (Ang)
In the WSI example,
f3 (Lpi) = Lpi / (2 * square (2))
f4 (Ang) = Ang + 45 (assuming that the angle is expressed in degrees)
End users generally do not expect to change the borders and angles to improve the end user's print tonal scale. An effective method here is to apply an inverse transformation formula to the requested screen borders and angles.
Lpi = ^f3-1 (desired Lpi)
Ang = ^f4-1 (desired Ang)

This formula gives us new borders and angles to calculate (or extract from the database) the traditional screen for each requested border and angle. For flexo printing, where the industry has long solved how to create traditional screens at most arbitrary borders and angles, to the extent that it makes sense, the required borders can be around 150 lpi. Whereas many, the conversion has a scale between 2.5 and 3 (2 * sqrt (2) for WSI). This will result in the construction of a screen of approximately 400 lpi with a resolution of 4000 ppi, which is well within the reach of current screening techniques.

For most patterns (especially WSI and DDWSI above), this conversion displays a screen that has already been shown to be working well. The flexo angle (7.5, 22.5, 37.5, 52.5, 67.5, 82.5) is accidentally converted to itself or another angle in the flexo set (eg 22). .5 is converted to 67.5 where the screen set already exists).

Conversions with even greater scaling effects may not be practical, but conversions are mostly of interest, as they correspond to lower solid pattern frequencies and less concentration enhancements. Not.

As described above, the disclosed method has the following features.
-Any ruled line or angle can be reached.
-The moire effect does not occur due to the systematic loss of pixels or the displacement of pixels.
The solid pattern is the same as the pattern determined by the conversion only if and only if the conventional screen from which the conversion is made is 100% totally black (as is usually the case).
-Of the pixels other than the pixels judged by the high resolution grid, none of them are always "black". This means that all the dots in the resulting digital film are "individual" and that all eight adjacent pixels are white.
The virtual shape of the new screen has something in common with the original screen shape within the limits imposed by the pixels that can be imaged.

Avoiding Colors Overlapping Moire It is well known that when creating three screens for CMYK colors, the borders and angles need to be carefully selected so that the resulting interference pattern does not have secondary moire. .. The formula for this is described, for example, in US Pat. No. 5,155,599 of Delabastita. This U.S. Patent Gazette is incorporated herein by reference in its entirety.

The disclosed transformations change the borders and angles, so if not performed carefully, there is a risk of moiré between the colors. The following algorithm avoids the occurrence of moire.
a) Start with the requested set of borders and angles.
b) Convert this according to the above equation.
c) In this set, find an exact matching ruled line / angle set with no secondary moiré. Depending on which technique is used, this is generally possible at less than 1% on the border and less than 0.1 degrees with respect to the angle.
d) Generate three screens.
e) Convert three screens according to the above algorithm.

The above approach works because the converted screen moiré frequency is converted in the same way as the original frequency (due to the pure reason of interferometric mathematical linearity). The above Delabastita formula refers to a moiré period that is actually infinite (0 in the equation refers to the moiré frequency, and the period is the reciprocal of this). By this conversion, the moiré will be divided by the frequency conversion coefficient of WSI (2 * sqrt (2)). Dividing infinity by any real number does not change it to infinity, so the converted screen set does not include quadratic moiré.

An important detail is the shape of the rosette. This is determined by the linear shift of the center of the dots compared to each other. Overlaying all dot centers on the origin creates a rosette centered on the dots, while a rosette with an empty center that is accepted requires one shift of color (mainly black) that covers half of the cell's square. And. This is also done for the rosette shift distance, as both distances are converted by frequency factor and angle shift.

Alternative configurations Many alternatives to the above methods can be constructed. For example, in the first alternative embodiment, a simple method for generating a high resolution basic pattern may be combined with other aspects of the improved method described herein. For example, the drilling method may be applied after a simple multiple formula (X'= X * 2, Y'= Y * 2). The result is a combination of good and bad from both methods and should be seen as a compromise. In the second alternative embodiment, it is possible to calculate an entirely new screen that applies the best embodiment of screen design to the modified pixel grid. In fact, the best examples of screen design are generally developed for pure square pixel grids, but the goal is primarily to easily shift to other grids. For example, an attempt to keep all screen dots of equal size can be made on an alternative pixel grid. Managing the Fourier transform of the screen is only somewhat more complicated than the above method and is not a problem for modern computer power.

The methods described herein operate at all gradation levels and, as a result, can be used over the entire tonal range. However, it is not necessary to use it in the entire color tone range. Certain users may only want to apply this technique to a certain degree, rather than extreme highlighting. In a preferred embodiment, the technique applies to at least 100-20% of the region. Below 20%, depending on the printing environment, indicate whether to use the techniques described herein, the highlighting enhancement techniques known in the art, or a combination thereof. May be good.

Therefore, here, a method including a highlighting improvement technique will be described. The new method of the present invention includes an original screen already including highlighting improvement techniques (eg, hybrid screening such as Esko Samba screen, Esko PerfectHighlight screen, HDFlexo screen, FM-like modulation in highlighting). It is possible to convert it to a new screen.

The new screen formed according to the embodiment of the present invention is generated by translating each pixel of the origin, thereby also inheriting a dedicated highlight modulation (eg, virtual FM dots). This is shown in FIGS. 7A and 7B. FIG. 7A shows the original transition screen (Samba screen tones below the critical gradation level are modulated by removing dots), and FIG. 7B shows the new post-conversion of the original screen leading to the same modulation. Draw the screen.

However, for conversion to a high resolution grid, highlighting improvement technology parameters may require scaling (eg, via different transition points or minimum dot sizes). This simple method has the advantage of not creating discontinuities on the new screen, but it also limits highlighting to the use of high resolution isolated pixels.

Another method of improving highlighting is by fading the screen with improved highlighting into a new screen in a particular color range. First, a supercell with the desired border and angle is calculated. Using any of the prior art highlighting enhancement techniques, evenly sized supercells with exactly the same desired borders and angles are calculated. Modern screening techniques can, for example, use Esco's Screen Manager to generate the desired prior art screen properties as described.

Next, both supercells are combined with the third supercell as follows.
a) For each pixel, determine the cell to which that pixel belongs. For convenience of explanation, a is an element of the screen grid, and the screen grid is formed by screen ruled lines and angles. For AM screens, one cell is a placeholder for one dot. Determining which cell a pixel belongs to is performed by using pixel coordinates and determining which grid element is in those coordinates. Assigning pixels to screen cells is a mathematical operation based on the requested screen borders and angles. A simple method is to assign each pixel to the center of the screen dot closest to that pixel (it repeats at the edge of the supercell, so it takes into account the dots closer to it). This is the prior art used in many screen calculation algorithms.
b) Determine from which of the two supercells the information is to be copied based on the cell. This determination may be purely random, for example using a blue noise determination, or systematic (eg, in a checkerboard pattern).

The above steps may be performed on the entire threshold array or separately for each bitmap array found by crossing both threshold arrays with the current threshold. In this case, the result is usually not a threshold array, but needs to be stored as a bitmap array set and used by the RIP bitmap array screen method. This functionality is established in modern advanced PDF RIP. As is known in the art, a threshold array represents the threshold of each pixel in a repeating tile, which is the order in which the pixels need to be turned on or off at the final two-layer output. Determine the key level. Such an array can also be represented as a bitmap array. At that time, each bitmap represents a pixel that is switched on for one gradation level. Therefore, another way to integrate the original supercell into a new supercell is to first convert both threshold arrays to bitmaps, create one bitmap for each gradation level, and then Applying steps by integrating bitmaps into. The new screen is represented as a series of bitmaps. Multi-threshold array bitmaps may be used in alternative embodiments, for example with more advanced RIPs, such as Esko FlexRIP and Esko Imaging Engineering. In such a bitmap, each pixel can have multiple thresholds (pixels can be switched on and off multiple times with different thresholds). In systems with such performance, the integration of different screens may result in a single multi-threshold bitmap instead of multiple bitmap arrays.

In one embodiment of the previous method, the higher density (eg, 20%) is near the first supercell and the lower density (eg, close to 0%) is near the second supercell. Includes staying in. In this way, a smooth transition appears between the newly proposed screen and the well-known features of prior art highlighting improved screens.

The possible results are shown in FIG. 6A. FIG. 6A is composed of dots based on a conventional screen (continuous dots 600 on a conventional grid) and dots based on a newly proposed screen (a collection of three pixels standing apart on a distributed grid 602). Indicates the type of screen dot.

In another example, blue noise may be applied without (or with an empty supercell) a second supercell. The results shown in FIG. 6B include a dispersed collection of dots 700 according to the present invention and are stochastically spread in space. In this method, the highlighting effect (FM-like modulation) is implemented directly on the new screen. For example, to obtain tones below the critical gradation level, the virtual dots are no longer reduced in size, but are gradually removed by the blue noise method (eg, using Esko Samba screen technology).

It is also possible to apply different patterns in the mixture. Using the same technique as described above, supercells with two different distributed grid patterns 800 and 802 may be combined, as shown in FIG. In a combination of different patterns, each of the two different distributed grid patterns correlates with each other so that the combination of patterns does not violate the distributed rules of the integrated screen (all pixels must be separated). Examples of the two compatibility patterns include the DDWSI and WSI patterns. These two patterns are interpreted as follows.
X_WSI = X_DDWSI + Y_DDWSI
Y_WSI = X_DDWSI-Y_DDWSI
Such patterns can be integrated in at least two ways:
1. 1. A new screen is generated using the conversion to convert to WSI. The DDWSI pattern is integrated into the cell-based criteria (eg, for blue noise, DDWSI is applied first to the cells that are farthest from each other) by adding missing pixels to the WSI grid.
2. 2. A new screen is generated using the conversion to convert to DDWSI. WSI patterns are integrated on a cell-based basis by removing pixels in the DDWSI grid.

Another method is to combine WSI dots with "normal" solid AM dots starting at a certain threshold. See FIGS. 11A and 11B for the advantages of combining "normal" continuous AM dots with "WSI" dots containing isolated pixels (reducing the number of exposed pixels by 8). I can understand. As shown in FIG. 11B, where the dot size is smaller, the WSI dot contains only four exposed pixels, so only four gradation levels are possible, and the dots are "square", whereas FIG. 11A The conventional AM dots shown in the above have 20 pixels, and thus 20 gradation levels, with an even better ability to approach a more rounded shape.

When a dot becomes smaller than a specific surface or the color tone to be expressed falls below a certain threshold value, the dot is replaced with a WSI pattern having a solid dot. Ideally, the transition from WSI dots to solid dots should be performed in a way that minimizes detection by the human eye. One way to do this is to gradually replace the WSI dots with optimally distributed solid dots so that the dots farthest from each other are replaced first using the farthest algorithm. Be done. For this reason, in the exemplary embodiment shown in FIG. 12, WSI dots begin to be replaced by AM dots of a particular size, i.e., AM dots in a color tone in which the WSI dots have 6 pixels. When the color scale is further lowered, the WSI dots of 5 pixels and 4 pixels are replaced with AM dots, and the size of AM dots is also reduced. Even lighter tones with only solid AM dots remaining may employ other highlighting improvements techniques, including the use of FM techniques with dot removal, as described herein.

Ideally, the print dot size of the WSI dots should be equal to the print size of the AM dots. Therefore, a WSI to AM size ratio is identified, which indicates the ratio of WSI dots to AM dots that replace WSI dots (eg, a 4:20 ratio includes 20 pixels of 4 WSI dots). Indicates that it will be replaced by AM dots).

This ratio can depend on printing conditions and is empirically determined by printing different ratio screens and choosing a ratio that does not cause a visible transition for a given set of conditions. obtain. For example, as shown in FIGS. 13A and 13B, solid dots are printed with dots of the same size as WSI dots at a ratio of 4:20 for the particular printing conditions used, so transitions are not visible. At this time, highlighting effect techniques such as support dots known to be used with solid dots or AM dots can be used below the threshold at which all dots are solid.

To mix WSI and solid dots, the screen may be displayed in a multi-threshold array (or a single multi-threshold bitmap) so that any pixel in the bitmap can have one or more threshold levels. can. For example, in order to display solid dots in pale shades, it is necessary to connect pixels to each other to form a specific dot size. To increase the tint and dot size, further at a higher threshold until the WSI / solid transition point (at which transition point the dots become WSI dots with isolated pixels, so certain pixels switch off again). Many pixels are turned on. The AM dots that replace the WSI dots are co-located (ie, the dot center of the AM dot is on the same screen grid as the center of the WSI dot). To obtain this, AM dots may be generated from the spot function rather than by integrating the AM screen into the WSI screen. At each WSI dot center position, the AM spot function determines the appropriate threshold so that a particular circle is obtained using the appropriate tonal modulation.

This method is not limited to the original AM screen. The described embodiments may be used to completely transform a stochastic screening supercell into a new one with all dots on a high resolution distributed pixel grid. In such an embodiment, as in the case of AM screening, the "apparent" ruled lines are reduced. Thus, for example, high frequency patterns such as those used with high quality offsets may be converted with much lower frequency results that are more practical for flexographic printing. As shown in FIGS. 9A and 9B, this method can be applied to any supercell screen, any bitmap array screen, and is easily extended to screening any shape.

Laser Tuning The screening patterns described herein with characteristic basic patterns are ideally used in combination with an imaging unit capable of pixel enhancement. Laser modulation to control the size of each underlying element of the basic pattern (eg, isolated pixels) is adjusted or optimized to maximize ink retention characteristics for each set of printing conditions (ink, substrate, temperature, etc.). Please understand that you can. For example, the ESKO CDI units described herein may have a controllable amount of enhancement between 100 and 400% of the laser "normal" intensity (power).

The laser system can be programmed to identify isolated pixels using a detection algorithm, such as using a 3x3 structural block as shown in FIG. The same structure is a single pixel by looking for a centrally exposed pixel with exposed adjacent pixels that is (a) present only in both the northwest and southeast corners or (b) only in both the northeast and southwest corners. It can be used to identify the diagonal (which may be augmented).

For this reason, the screen containing the WSI dots described herein ideally detects isolated pixels when creating a mask with software for generating the desired digital pattern and determines the size of the isolated pixels. It is performed in combination with an exposure system programmed to adjust. This mask is then ideally used to create a print plate using a system designed to create a flat top pixel structure, as is known in the art. One exemplary imaging device programmable to enhance isolated pixels to create masks with microcells as described herein is Esko-Graphics Imaging GmbH, located in Itzehoe, Germany. It is a CDI digital imaging device manufactured by the company, and GRAPHOLAS (version 10.3.0 or higher) software is installed to create flat top dots. In particular, Esco's "Full HD" and CDI crystal systems with pixel boost and in-line UV capabilities are ideal for performing the steps described here. Increasing the number of isolated pixels brings the resolution to a fine-tuned level that is generally not available by using screen features alone. Such tweaks allow for the definition of gradation on the screen and the ink transfer capability defined using hardware modulation.

Although described herein in the context of Esco hardware, the invention is not limited to the system of a particular manufacturer. Systems that create flat top dots using UV exposure are known in the art. In Esco systems, for example, such systems include specific UV heads and servos capable of rotating the drum at the desired speed, and high resolution optical systems such as gradient index lenses or aspheric focal lenses. May be equipped. The use of flat top exposure is particularly desirable as it maintains exposure to the top of the plate and creates more prominent "holes" to fill the ink when the plate is created from its mask. In general, it is possible to use a UV head that does not imitate bank light and does not have a wide angular distribution.

The systems that can be used to generate the desired printing plate properties as described herein are not limited to the exemplary systems considered herein. As used herein, the term "mask" may refer to any type of structure used during the printing plate exposure step. However, although a UV exposure system for making masks is shown and described herein, a laser system for directly removing the printing plate material also has the desired effect on the printing plate. As such, it may be programmed to modulate the laser output. It is not limited to laser exposure, and any method for adjusting the aperture size on the mask may be used. Similarly, any using a mask or the like that can transform the screen information in such a way that the screen information produces the desired printing plate structure corresponding to the screen having the ink transfer characteristics resulting from the screen information. The plate-making method can be used in conjunction with the screen structure described herein.

Printed matter produced using the printing plates produced by the systems and methods described herein tend to have a dot gain that is independent of screen borders, and the dot gain curve has minimal tonal skipping. Have. This technique also minimizes dot cross-linking.

It is described herein in connection with a screen having the WSI structure described herein (ie, a high resolution basic pattern of isolated dots), and it is advantageous to use such a screen in combination with laser enhancement. However, the desired ink transfer characteristics are physical on the printing plate or mask corresponding to the screening spots so that each set of four adjacent physical spots in the basic pattern has an unexposed area in the center between them. It may be generated using any system that can be adjusted to selectively adjust the size of the spot. For example, as shown in FIG. 15B, laser exposure of individual pixels is typically selected to provide overlapping spots that cover the entire solid area. However, laser modulation may be used to reduce the spot size corresponding to each exposed pixel so that the unexposed area occurs in the center of the four adjacent spots, as shown in FIG. 15C. As shown in both FIGS. 15A and 15C, the spots formed by the laser do not overlap as a whole as in FIG. 15B. Although the contact of the spots is depicted in FIG. 15A, the solid ink density is adjusted to less than the maximum value, but when the uniformity of the ink film on the substrate is the same, a configuration in which the spots do not contact can be used. Please note. For this reason, for example, instead of creating a high resolution screen with isolated pixels, the structure in which a low resolution screen is actually imaged, regardless of screen dot size, is the ink transfer discussed herein. It may be used with laser modulation that ensures that it contains a small unexposed area that provides advantages.

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not limited to the details shown. Rather, various changes can be made to the scope and details within the scope of the claims without departing from the present invention.

Claims (12)

It is a method of making a flexographic printing plate, and the above method is
(A) A step of providing image information in the form of a screen having a plurality of screen pixels corresponding to an ink-supporting portion and a non-ink-supporting portion of the flexographic printing plate, wherein the ink-supporting portion is a plurality of ink-supporting portions. With elements, steps and
(B) A step of forming an imaged individual element and a non-imaged individual element according to the image information.
(I) A step of superimposing a basic pattern of spots having uniform dimensions on the screen pixels of the image information, and each spot is formed into an imaged individual element or a non-imaged individual element represented on the flexographic printing plate. Each spot corresponding to the imaged individual element in the basic pattern is surrounded by eight spots corresponding to the non-imaged individual element, and corresponds to the imaged individual element and the non-imaged individual element. The spots are aligned with the grid formed by the imaging resolution of the imaging device, the steps, and
(Ii) A step of selecting a size to form each imaging individual element such that each set of four adjacent imaging individual elements has a non-imaging individual region located at the center thereof, at the center. The located non-imaging individual regions are decomposed into regions on the surface of the flexographic printing plate having a height within the flexographic printing plate that is below the top height but above the non-printing height. By a step, where each of the adjacent imaging individual elements is decomposed to the top height.
The steps to form the element and
How to include. The method of claim 1, wherein each spot of the basic pattern has a size corresponding to the size of the smallest imaging individual element formed by the flexographic printing plate or mask. The method according to claim 1, further
A step of creating a mask for use in the exposure of the flexographic printing plate and a step of exposing the flexographic printing plate through the mask are included.
The method comprises creating an image on the mask corresponding to each imaging individual element and each non-imaging individual element on the flexographic printing plate. The method of claim 3, wherein each of the imaging individual elements corresponds to the spatial resolution of the laser beam used to form the corresponding image on the mask, wherein the method is the laser beam. A method comprising forming an image on the mask by. The screen comprises one or more isolated pixels and one or more non-isolated pixels.
The step of imaging the mask with the laser beam enhances the output of the laser beam used to image each isolated pixel relative to the output of the laser beam used to image the non-isolated pixels. 4. The method of claim 4, comprising the step of performing. (A) A step of forming a first screening supercell comprising a plurality of first screen pixels, wherein each first screen pixel has a solid or empty first screen pixel value.
(B) For each pixel having a solid first screen pixel value located at (X, Y) of the first screening supercell, the first formula X'= fx (X, Y).
Y'= fy (X, Y)
By applying a step of assigning a position (X', Y') to a second screening supercell containing a plurality of second screen pixels, each of which has a solid or empty second screen pixel value.
(C) The plurality of the second screening supercells such that the second screen pixel having no value set by the first formula is set to an empty second screen pixel value. A step of setting a second screen pixel value for a pixel,
In the first formula, (i) X'and Y'are integers, and (ii) any two first screen pixels of the first screening supercell are the same in the second screening supercell. All second screen pixels (X', Y') that are not converted to second screen pixels and have (iii) solid values have at least an empty value that is not set by the first equation. Includes a step that adheres to a set of rules that eight empty second screen pixels form the basic pattern of spots surrounding each pixel (X', Y') having a solid value. , The method according to any one of claims 1 to 5. An imaging system that manufactures a mask that exposes a flexographic printing plate, and the imaging system is
A laser source configured to emit a laser beam to expose a portion of the mask to the radiation corresponding to the imaging individual element corresponding to the spot of uniform size specified in the imaging data file. The laser source comprises a laser source having an adjustable laser output that adjusts the size of the laser beam that exposes the imaging individual element with the mask.
A controller comprising a processor configured to receive imaging data and convert it into operational instructions for the laser source, the imaging data corresponding to ink-bearing and non-ink-bearing portions of the flexo printing plate. The ink-bearing portion comprises imaging data including image information in the form of a screen having a plurality of screen pixels, the ink-bearing portion comprises a plurality of ink-bearing elements, and the imaging data is superimposed on the screen pixels of the image information. In the controller, which includes a basic pattern composed of the spots, where each spot corresponds to an imaging individual element or a non-imaging individual element represented on the mask.
Each spot corresponding to the imaged individual element of the basic pattern is surrounded by eight spots corresponding to the non-imaged individual element.
The spots corresponding to the imaging individual elements and the non-imaging individual elements are aligned with the grid formed by the imaging resolution of the imaging device, and the controller corresponds to the non-solid color tone region of the flexographic printing plate. The mask is configured to create the mask by forming each imaging individual element with the laser beam in at least a portion of the mask, the size of the laser beam being four adjacent imaging individual elements. Each set of should have a non-imaged individual region in the center between them.
The non-imaging individual region on the mask has a height within the flexographic printing plate that is below the top height but above the non-printing height on the flexographic printing plate exposed using the mask. An imaging system comprising a controller that is decomposed into regions on the surface of the flexographic printing plate and each of the four adjacent imaging individual elements is decomposed to the highest height. The controller is configured to identify each spot corresponding to the imaged individual element of the basic pattern surrounded by the eight spots corresponding to the non-imaged individual element as an isolated spot.
An output larger than the output of forming the imaged individual element corresponding to the isolated spot of the imaged data is used in the laser source to form the imaged individual element corresponding to the isolated spot of the imaged data. 7. The imaging system according to claim 7, wherein the imaging system is configured to instruct. Each of the set of the four adjacent imaging individual elements in the set of the imaging individual elements has a circular periphery that does not overlap as a whole at the periphery of another imaging individual element in the four sets. Item 8. The imaging system according to item 8. The imaging system is a UV exposure system that exposes a flexo printing plate with UV radiation in a pattern corresponding to the mask, and the UV exposure system is configured to produce flat top dots. The imaging system according to any one of claims 7 to 9, further comprising. It is a flexographic printing plate, and the flexographic printing plate is
It comprises an ink-supporting portion and a non-ink-supporting portion of the flexographic printing plate corresponding to image information in the form of a screen having a plurality of screen pixels.
The ink-carrying portion comprises a plurality of ink-carrying elements, including a basic pattern of spots of equal size, superimposed on the screen pixel of the image information.
, Each spot corresponds to an imaged individual element or a non-imaged individual element represented on the flexographic printing plate.
Each spot corresponding to the imaged individual element of the basic pattern is surrounded by eight spots corresponding to the non-imaged individual element.
The spots corresponding to the imaging individual element and the non-imaging individual element are aligned with a grid formed by the imaging resolution of the imaging device, and each set of four adjacent imaging individual elements is in between. Have a centrally located non-imaged individual region,
The centrally located non-imaging individual region is decomposed into regions on the surface of the flexographic printing plate having a height within the flexographic printing plate that is below the top height but above the non-printing height. Each of the four adjacent imaging individual elements is decomposed to the maximum height.
Flexographic printing version. The flexo printing mask for exposing the flexographic printing plate according to claim 11, wherein the flexo printing mask includes a plurality of images on the flexo printing mask, and each image is each on the flexo printing plate. A flexographic printing mask that corresponds to an imaged individual element or a non-imaged individual element.

Images